The present invention relates generally to ultrasonic imaging catheters, and more particularly, to improved ultrasound imaging assemblies and methods of making same.
Intravascular imaging of blood vessels and surrounding tissues continues to be of great benefit in a wide range of medical fields. A particularly successful design for an intravascular imaging catheter is shown in FIG. 1. The catheter 10 employs a rotatable imaging assembly 12 containing an ultrasound transducer 14, where the assembly is attached to the distal end of a flexible drive cable. A flexible sheath 18 is inserted into a patient, and the drive cable and imaging assembly are inserted into the sheath. The transducer may be rotated in order to transmit an ultrasound signal and produce a video image by well-known techniques.
To produce images, it is desirable to have ultrasound signals 20 transmitted by the transducer pass through the sheath (as shown by arrow 22) and reflect off of tissue or fluids. However, a portion of the ultrasound signals transmitted by the transducer typically are reflected by the sheath (as shown by arrow 24). The amount of signal reflected typically is greatest when the angle of incidence between the signal and the sheath is about 90 degrees. Hence, as shown in FIG. 1, it is desirable to tilt the transducer relative to the sheath, thereby reducing the amount of reflected signal.
Angling the transducer typically involves forming a hole 16 in the assembly at the desired angle. However, the formation of an angled hole, particularly in such a diminutive assembly, presents difficulties. For example, angled holes typically have irregularities caused by the hole formation technique. The transducers often are placed and affixed by hand, which can lead to variations in transducer alignment between otherwise identical assemblies.
It is desirable, therefore, to provide imaging assemblies with firmly affixed transducers positioned at the proper angle relative to the sheath. It also is desirable to provide imaging assemblies that are easier to manufacture, and have greater consistency from assembly to assembly.